A patient presents with monocytosis and hypercellular marrow showing monocytic and granulocytic dysplasia; BCR-ABL negative. Which diagnosis fits best?

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Persistent monocytosis with dysplasia affecting both monocytic and granulocytic lineages in a hypercellular marrow points to a clonal myeloid neoplasm that blends dysplasia with myeloproliferation. This pattern is classic for chronic myelomonocytic leukemia, a myelodysplastic/myeloproliferative neoplasm characterized by sustained monocyte expansion and dysplasia without the BCR-ABL1 fusion. The BCR-ABL negative status helps distinguish it from chronic myeloid leukemia, which typically shows marked granulocytic proliferation driven by BCR-ABL. Acute myeloid leukemia would require a high blast percentage, which isn’t described here. Hairy cell leukemia would present with characteristic hairy cells on morphology and a different clinical/immunophenotypic profile, not the monocytosis with multilineage dysplasia described.